in the united states today, universities can no longer take advantage of the research exemption https://en.wikipedia.org/wiki/Research_exemption to patents because madey v. duke held that, by using madey's patented invention for research purposes, duke was 'increas[ing] the status of the institution and lur[ing] lucrative research grants', so a sneaky lawyer hired by a hypothetical future cacm administration could argue that things like archiving the cacm articles in a university library could produce 'commercial advantage' for the university, so it would be nice to have the acm using language that protects users' rights more solidly
also, i feel like having the notice hidden by default makes it unnecessarily difficult to comply with, since the notice requires that copies 'bear this notice (...) on the first page'. unlike older cacm publications, the pdf of that article produced by the acm also doesn't bear the notice on the first page, or in fact anywhere, so you have to modify the pdf to be able to copy it in compliance with the conditions of the notice
cc-by-nd or similar licenses are clearly not compliant with the definition of 'open access' in the berlin declaration. you may be correct that acm doesn't have the legal ability to license the creation of derivative works of older articles unless the author or other copyright holder had transferred copyright to the acm. that would make those older articles not open access, and obtaining the necessary licenses might be logistically infeasible at this point by any measure short of drastically reducing the term of copyright through legislation
so it seems like the acm is improving the situation considerably, but there's still a long way to go